Anti-reflash dry chemical agent

ABSTRACT

A DRY POWDERED, FIRE EXTINGUISHING COMPOSITION IS PROVIDED WHICH COMPRISES A CONVENTIONAL FIRE EXTINGUISHING, POWDER BASE MATERIAL, SUCH AS AN ALKALI METAL BICARBONATE OR THE LIKE, HAVING A FLUOROCARBON SURFACTANT ADSORBED ON ITS SURFACE. THE FLUOROCARBON SURFACTANTS HAVE THE FORMULA CNF2N+1CO-Z OR CNF2N+1SO2-Z. THE FLUOROCARBON SURFACTANT IS ADSORBED ON THE POWDER BASE MATERIAL BY SLURRYING A SURFACTANTSOLUTION OR MILLING A POWDERED SURFACTANT WITH THE POWDER BASE MATERIAL.

United States Patent 3,553,127 ANTI-REFLASH DRY CHEMICAL AGENT William R. Warnock, Menominee, Mich., and Donald V. Flatt, Hudson, and John R. Eastman, Marinette, Wis., assignors to The Ansul Company, Marinette, Wis., a corporation of Wisconsin No Drawing. Continuation-impart of application Ser. No. 638,574, May 15, 1967. This application Feb. 6, 1969, Ser. No. 797,232

Int. Cl. A62d 1/00 US. Cl. 252 16 Claims ABSTRACT OF THE DISCLOSURE A dry powdered, fire extinguishing composition is provided which comprises a conventional fire extinguishing, powder base material, such as an alkali metal bicarbonate or the like, having a fluorocarbon surfactant adsorbed on its surface. The fluorocarbon surfactants have the formula C F2 +1COZ or C F3 S02Z.

The fluorocarbon surfactant is adsorbed on the powder base material by slurrying a surfactant solution or milling a powdered surfactant with the powder base material.

This application is a continuation-in-part of US. patent application Ser. No. 638,574, filed May 15, 1967, now abandoned.

This invention relates to dry chemical fire extinguishing agents. More particularly, it relates to dry, free-flowing, powdered fire extinguishing agents which are effective to extinguish fires in flammable liquid hydrocarbons and to inhibit reignition or reflash of unburned portions of such liquid hydrocarbons.

In the past, two diverse types of fire extinguishing agents have been used in combatting fires in flammable liquids (Class B fires). The agents generally used for such purposes are either dry chemicals or foams. Each of these types of agents have undesirable shortcomings, however, and many attempts have been made to overcome these deficiencies.

For example, although dry chemicals such as sodium and potassium bicarbonate and the like are highly effective extinguishing agents, and achieve a rapid extinguishment of flames in burning liquid hydrocarbons and the like, even with relatively small quantities of the extinguishing agent, the dry chemical agents heretofore used do not provide any lasting securing effect. Thus, once the supply of dry chemicals is exhausted, unburned portions of the fuel can be easily reignited by any unextinguished fire or by some extraneous source of ignition, e.g., sparks, heat and the like.

This lack of securing effect of the dry chemical-type agents is due to their failure to achieve retention at the surface of the burning liquid. The powder is wetted as it falls into the liquid, and since it is more dense than the liquid, it sinks below the surface. Once the powder falls below the liquid surface, its extinguishing or flame-inhibiting action is effectively lost.

Many of the deficiencies of prior art powdered chemical fire extinguishing agents are avoided by the use of foam-type agents. Thus, it is possible to extinguish fires in burning liquid hydrocarbons and the like with the foamtype extinguishing agents which provide a highly effective 3,553,127 Patented Jan. 5, 1971 securing action and substantially prevent reignition of the unburned portion of the fuel. Various types of foam extinguishing agents have been heretofore proposed for such purposes, including protein foams and surfactant foams.

These foams extinguish the flames by spreading over the surface of the flaming liquid to cut off the supply of flammable vapors feeding the fire. This mechanism requires that the foam be applied to the fuel surface and allowed to flow over the entire burning area. This requirement greatly impedes rapid extinguishment of the fire, and thus foam-type fire extinguishers are generally characterized by undesirably slow operation.

Because of the various shortcomings of both the dry chemical and foam-type extinguishing agents, it has been proposed to utilize foam and dry chemical extinguishers in combination in order to obtain the advantages of both systems. Such a dual system is described in US. Pat. 3,258,423 to Tuve et al. Although such dual systems have many attributes, they are not entirely satisfactory, because they require separate dispensing means for each of the extinguishing agents, and thus require the use of complex extinguishing devices which are difficult to use in the effective application of extinguishing agents to a fire.

For example, twinned systems are often clumsy and diflicult for a single operator to handle, Moreover, the simultaneous use of dry chemical extinguishers and foamtype extinguishers can be adversely affected by incompatibility of the two types of agents, which often results in breakdown of the foam when it is brought into contact with the dry chemical extinguishing agent.

Accordingly, it is the primary object of the present invention to provide an improved fire extinguishing compo sition which effectively extinguishes flammable liquid fires and secures this extinguishment by inhibiting reignition or reflash of the unburned portion of the flammable liquid.

Another object of the present invention is to provide a dry, powdered fire extinguishing composition which rapidly extinguishes burning liquid fires and also acts as a barrier to prevent reignition of the unburned portion of the liquid after the tire is initially extinguished.

Still another object of this invention is to provide a dry, powdered fire extinguishing composition which rapidly extinguishes flames in burning liquids, which is resistant to Wetting by such liquids, and which is retained at the surface of the burning liquid to inhibit reignition.

Yet another object of the present invention is to provide a single anti-reflash fire extinguishing composition which provides both extinguishment and securing action and which can be applied readily to burning liquids from a single unit dispensing system of the type in conventional use with dry chemical extinguishing agents.

A further broad object of'the present invention is to provide a dry chemical fire extinguishing agent which has anti-reflash properties which enable it to secure extinguishment of fires in flammable liquids.

A still further object of the present invention is to provide a method for extinguishing fires in flammable liquids with the improved fire extinguishing agents of this invention.

Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention, the objects and advantages being realized and attained by means of the 3 instrumentalities and combinations particularly pointed out in the appended claims.

To achieve the foregoing objects and in accordance with its purpose, as embodied and broadly described, the present invention provides a free-flowing, powdered, fireextinguishing composition capable of both achieving the rapid extinguishment of burning flammable liquids and securing this extinguishment by inhibiting reignition of the unburned portions of the liquid. This fire extinguishing composition comprises a dry powder capable of extinguishing flames at the surface of burning liquids, the powder having adsorbed thereon a fluorocarbon surfactant having a formula selected from the group consisting of:

C F CO-Z and CHFM Z-Z where n is an integer from 3 through 9, and Z is a surface active group.

The present invention also provides a method .of extinguishing fires in flammable liquids which comprises covering the burning surface area of the liquid with a fire extinguishing agent of the type defined above.

The invention consists in the novel compositions, methods, processes and improvements shown and described.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory but are not restrictive of the invention.

The fire extinguishing composition of the present invention has as its base a dry powder capable of extinguishing flames at the surface of burning liquid fuels. This dry powder can comprise any of the conventional dry-chemical extinguishing agents, which are well known for their ability to rapidly extinguish fires in flammable liquids. Preferred examples of such powders include alkali metal bicarbonates, such as sodium or potassium bicarbonate, monoarnmonium phosphate, and alkali metal chlorides, such as sodium or potassium chloride. Other similar powdered extinguishing agents will readily suggest themselves to those skilled in the art. Sodium bicarbonate and potassium bicarbonate are particularly preferred powder bases for the extinguishing agents of the present invention.

In accordance with the present invention, the dry, powder base had adsorbed on its surface a fluorocarbon surfactant having a formula selected from the group consisting of:

wherein n is an integer from 3 through 9, and Z is a surface active group.

It has been found that treatment of the surface of the powder particles forming the base of the present composition with these fluorocarbon surfactants produces freeflowing, powdered fire extinguishing compositions which are resistant to wetting by liquid fuels and produce a barrier or film over the surface of burning fuels which substantially reduces or retards evaporation of flammable vapors and thereby substantially inhibits reignition of the unburned portion of the fuels.

As shown by the above formulae, the fluorocarbon surfactants used to produce the fire extinguishing agents of the present invention are derivatives of perfluorocarboxylic and perfluorosulfonic acids. The surfactants are composed of molecules containing a per-fluorinated head portion and a surface active tail portion. The fluorocarbon portion of the molecules advantageously contain 7 carbon atoms where the surfactant is a perfluorocarboxylic acid derivative, and 8 carbon atoms where the surfactant is a perfluorosulfonic acid derivative. Thus the preferred surfactants have the formulae:

The surface active Z portion of the fluorocarbon surfactants adsorbed at the surface of the powdered fire extinguishing agent composition can be an OM group, in which M is ammonia or an alklai metal, or an NR group, in which one or both Rs can be hydrogen, alkyl, alkyl amine, alkyl quaternary ammonium ion, betaine type quaternary, alkanol, alkanol sulfate, alkanol sulfate salt, alkyl carboxylic acid, alkylcarboxylic acid salt, and the like. The surface active Z portion of the fluorocarbon surfactant is preferably NHR, with R one of the groups just described.

Exemplary fluorocarbon surfactants which can be used to produce the improved compositions of this invention are identified by the numbers 1 through 7 in Table I.

TABLE I and Mixtures of two or more of such surfactants can, of course, also be used and are preferred.

A number of the above listed fluorocarbon compounds, and other similar compounds which are also suitable for use in the preparation of the fire extinguishing compositions of the present invention, are sold as concentrates.

The fire extinguishing composition of this invention can be prepared by slurrying the dry powdered base material with a solution of the fluorocarbon surfactant in a suitable solvent or diluent, such as water, methanol, isopropanol, acetone, methylethyl ketone, or the like The powder absorbs the fluorocarbon surfactant during this slurrying procedure, and the resultant product is filtered, dried, and then screened through an appropriate screen to produce a free-flowing powder product of the desired size.

It is also possible, in some cases to mill the fluorocarbon surfactant in a dry state with the powdered base material to impart the desired wetting resistance and surface retention properties to base material.

The final powdered product can be of any desired particle size, although it is generally preferred that the powder be small enough to pass through a IOO-mesh screen. The amount of surfactant adsorbed on the powdered base material will, of course, depend on the particular fire extinguishing powder base material and the particular surfactant selected. It is preferred to slurry the powder base and the surfactants for a period sufli cient to achieve the maximum adsorption possible with each particular combination of base material and surfactant. The preferred procedure generally produces a fire extinguishing composition comprising 0.00001 to 10%, preferably 0.05 to 3% by weight of the adsorbed fluorocarbon surfactant, the remainder being the dry powder base.

The foregoing procedures produce a free-flowing, powdered, dry-chemical fire extinguishing agent which provides the rapid extinguishing action of conventional dry chemical extinguishers, and also forms a film over the surface of burning fuels to inhibit reignition of unburned fuel once the flames initially present are extinguished. Even in cases where the flames are not completely extinguished initially, the application of the extinguishing agent of this invention greatly reduces the speed of the reflash of flames over the surface of the burning liquid. This allows the remaining flames to be extinguished with secondary or standby extinguishers.

The extinguishing compositions of this invention can be applied from a single unit extinguisher, rather than the more complicated twinned systems presently necessary to achieve a combination of rapid extinguishment and securing effect. The use of such single unit extinguishers makes application of the present composition simpler, faster, and more direct.

The provision of the improved fire extinguishing compositions of this invention in powdered form allows them to be applied from existing dry chemical extinguishing systems which have long been commercially available, and which have the advantage of simplicity of design and dependability of operation acquired over extended periods of use.

In extinguishing flammable liquid fires in accordance with the method of the present invention, a dry fire extinguishing composition of the type defined above is applied to a burning liquid to cover the area in flames. The application of the extinguishing agents of this invention almost immediately extinguishes the flames, and also either prevents or substantially inhibits reignition. Exemplary of the flammable liquids which can be treated for fire extinguishment in accordance with the method of this invention are gasoline, naphtha, kerosene, jet fuels, diesel oils, and the like.

The fluorocarbon surfactant-treated powders achieve initial extinguishment of the flame at about the same rate as untreated, conventional-type extinguishers. Thus the treatment of the powder base with fluorocarbon surfactants in accordance with the present invention in no way adversely affects the efficient extinguishment properties of the base material.

The present compositions, however, are both resistant to wetting by the burning fuel and retentive to the surface of the liquid. These properties enable the present compositions to achieve their anti-reignition protection.

The amounts of the present fire extinguishing compositions which are advantageously applied to the surface of a burning liquid will be apparent to those skilled in the art. For example, a gasoline fire of about 200 square feet can be extinguished by the application of about 30 pounds of a fire extinguishing composition comprising 25-micron potassium bicarbonate powder having adsorbed thereon a Light Water surfactant of the type described herein.

For a clear understanding of the invention, specific examples of it are set forth below. These examples are merely illustrative, and are not to be understood as limiting the scope and underlying principles of the invention in any way. All parts and percentages referred to herein are by weight unless otherwise specifically indicated.

EXAMPLE 1 Two grams of the fluorocarbon surfactant identified as (1) in Table I was dissolved in 100 ml. of acetone. To the resulting solution was added 100 grams of powdered sodium bicarbonate having a surface area of about 1400 cmP/gram. The resulting slurry was mixed thoroughly, and then filtered. The filter cake was air dried and screened through a 100-mesh screen. The powdered product was free-flowing and resistant to wetting by gasoline. On application to the surface of a pool of gasoline, it floated and spread over the surface to form a substantially impervious film. The gasoline would not ignite when a flame was passed over the surface and adjacent thereto.

EXAMPLES 2-7 Example 1 was repeated using the surfactants identified as 2 through 7, respectively in Table I. Similar results were achieved.

EXAMPLES 8-17 Example 1 was repeated using mixtures of the surfactants identified in Table I. Table II identifies the mixtures employed and the amount of each surfactant used in the mixture.

TABLE II Amount of surfactant/ Mixture of grams of NaH Example N 0. surfactant used" 003 1. 0 1 m 1 Is 5 .5

*Numbers in brackets refer to code number for surfaetants identified in Table I.

The powder resulting from each of Examples 8-17 when applied to the surface of gasoline floated on the surface and formed a continuous film thereon. In each instance, the gasoline would not ignite when a flame was passed over the surface and adjacent thereto. When the film was broken, as by poking a glass rod therethrough, the gasoline would fiash into fire when an open flame was passed adjacent thereto. The powdered particles, however, would immediately coalesce, to reform the film, thereby substantially instantaneously extinguishing the flame. The mixture of Example 17 was considered to provide the best anti-reflashcharacteristics of all the combinations tested.

The surfactant treated dry chemical powders of this invention finds important utility not only in fire extinguishing, but also in fire prevention. For example, such powders, when floated on the surface of a liquid hydrocarbon, e.g., gasoline or oil stored in tanks or in commercial receptacles, serve to prevent flash fires in the storage tanks and receptacles. Thus, in the fire prevention embodiment of the invention, tanks or other receptacles containing flammable hydrocarbons could be treated such that an exposed or upper surface of the liquid hydrocarbon has formed thereon an impervious film of the surfactant treated dry chemical powders of this invention.

In fire extinguishment, the surfactant treated dry chemical powders of this invention will be applied to the burning area of the flammable liquid in the conventional ways utilized to apply the dry chemicals. Typically, the surfactant treated dry chemical powders will be applied to the burning area of the flammable liquid until the surface of the liquid is coated with a film of the dry powder, thereby substantially militating against reflash. In flammable liquid stored in containers such that the liquid has an exposed surface within the containers, incipent fires may be prevented or their risk substantially reduced by forming at the exposed surface of the liquid in the containers a film comprising the free-flowing fire extinguishing compositions described herein.

What is claimed is:

1. A free flowing, powdered, fire-extinguishing composition capable of achieving the rapid extinguishment of burning flammable liquids and of securing the extinguishment by inhibiting reignition of unburned portons of the liquid, said composition consisting essentially of: a dry powder base material capable of extinguishing flames at 7 the surface of such burning liquids selected from an alkali metal bicarbonate, mono-ammonium phosphate and an alkali metal chloride, said base material having adsorbed thereon a fluorocarbon surfactant having a formula selected from the group consisting of:

wherein n is an integer from 3 through 9, and Z is OM wherein M is ammonia or an alkali metal or NR wherein each R is alkyl, alkylamine, alkyl quaternary ammonium ion, betaine type quaternary, alkanol sulfate salt, or alkyl carboxylic acid salt and said fluorocarbon surfactant is present in an amount of between about 0.00001 to by weight.

2. The composition of claim 1 in which the base material is sodium bicarbonate.

3. The composition of claim 1 in which the base material is potassium bicarbonate.

4. The composition of claim 1 in which the fluorocarbon surfactant has a formula selected from the group consisting of:

s n z m sHq),

including mixtures thereof.

5. The composition of claim 1 wherein the fluorocarbon surfactant is present in an amount of between about 0105 and about 3% by weight.

6. The composition of claim 1 in which the fluorocarbon surfactant has the formula 7. The composition of claim 1 in which the fluorocarbon surfactant has the formula C F CONH (CH N (CH 2 8. The composition of claim 1 in which the fluorocarbon surfactant has the formula and 8 9. The composition of claim 1 in which the fluorocarbon surfactant has the formula 10. The composition of claim 1 in which the fluorocarbon surfactant has the formula 11. The composition of claim 1 in which the fluorocarbon surfactant has the formula 12. The composition of claim 1 in which the fluorocarbon surfactant has the formula 13. A flammable liquid comprising an exposed surface coated with a film consisting essentially of the freeflowing powder fire extinguishing composition of claim 1.

14. A method of preventing incipient fires in flammable liquids stored in containers, such that the liquid has an exposed surface within the container which comprises forming at the exposed surface a film consisting essentially of the free-flowing powder fire extinguishing composition of claim 1.

15. A method of extinguishing a flammable liquid which comprises applying to the burning area of the liquid the fire extinguishing composition of claim 1.

16. A method of extinguishing a flammable liquid which comprises applying to the burning area of the liquid the fire extinguishing composition of claim 1, and continuing the application until the surface of the liquid is coated with a film of the composition.

References Cited UNITED STATES PATENTS 3,172,852 3/1965 Lobos 2525 3,214,372 10/1965 Lobos 2522X 3,258,423 6/1966 Tuve et a1. 2523 3,350,306 10/1967 Alleton 252-543 MAYER WEINBLATT, Primary Examiner U.S. Cl. X.R. 

